1. Field of the Invention
The present invention relates to a wire dot printer head and a wire dot printer provided with the wire dot printer head.
2. Discussion of the Background
In a wire dot printer head, plural cores with coils wound thereon are arranged radially, annular yokes are disposed inside or outside the cores, plural armatures which actuate wires are arranged so that they can rise and fall with respect to the cores, and the armatures are caused to rise and fall by energizing the coils, thereby causing wires to move at high speed toward a platen to effect printing.
In such a wire dot printer head, in order to effect printing at high speed and improve the print density, it is necessary that the spacing between a front end of the wire dot printer head (wire tips) and the platen, i.e., printing gap, and the stroke of each armature (a displacement quantity in the platen direction of wire) be adjusted depending on paper to be printed while being mutually taken into account.
For example, in case of using an ink ribbon, the printing gap in the wire dot printer head is set at a value which is obtained by adding a minimum gap necessary for smooth paper feed to the sum of paper thickness and ink ribbon thickness. When printing is performed for one sheet of paper, there accrues an advantage if the armature stroke is set to a minimum to increase the printing speed. When printing is performed for paper with carbon applied to the back side thereof or for a slip comprising plural superimposed sheets of a pressure-sensitive paper, it is necessary to make the armature stroke large even if the printing speed decreases, or else the pressing force of wire against the slip will become insufficient and the lower the paper position, that is, the closer to the platen, the smaller will be the pressing force of wire and lower the print density, so it is necessary to make the armature stroke large.
As to the method for adjusting such printing gap and armature stroke, it is described, for example, in Japanese Published Unexamined Patent Application No. Hei 9-1890. According to this method, both adjustment of the printing gap and adjustment of the armature stroke are performed simultaneously.
In the above method, however, a constituent member for adjusting the printing gap and a constituent member for adjusting the armature stroke are provided separately in the wire dot printer head and are interlocked with each other through an interlocking member. Consequently, the device configuration of the wire dot printer head is complicated and the manufacturing cost becomes high.
Accordingly, an object of the present invention is to provide a wire dot printer head and a wire dot printer both able to simplify the construction for the adjustment of armature stroke and printing gap and attain the reduction of cost.
The object of the present invention is achieved by the novel wire dot printer head and wire dot printer of the present invention.
In the wire dot printer head of the present invention, a spacer is inserted between a yoke block and a head holder. The yoke block comprises yokes opposed to plural armatures, coils wound respectively round plural cores which are opposed at one ends thereof to the armatures, and fulcrum portions which hold the armatures so that the armatures can rise and fall with respect to end faces of the cores. The spacer is adapted to move upon exertion of an external force thereon, thereby changing the spacing between the yoke block and the head holder. Thus, since the distance between the head holder and the platen changes, it is possible to adjust the printing gap. At the same time, since the armature-core gap changes, it is possible to adjust the armature stroke and hence possible to simplify the construction for the adjustment of armature stroke and printing gap and attain the reduction of cost.